This investigation has been proposed to study the metabolism of retinol and retinoic acid in different tissues of the rat. The turnover and half-life of retinol, estimated in retinoic acid supplemented rats, will be compared with those in retinyl acetate supplemented animals. The chemical characteristics of urinary metabolites of retinol and retinoic acid will be studied with a view to develop a specific method for detection of incipient vitamin A deficiency in animals and humans.